The present invention relates to a ceramic laminate body preferably applied to various gas sensors which are configured into a laminated or multilayered structure.
According to a conventional method, a ceramic laminate body with a closed hollow space therein is manufactured in the following manner.
Two similar ceramic green sheets (referred to first ceramic green sheets) and one other ceramic green sheet (referred to second ceramic green sheet) are prepared. The second ceramic green sheet and the first ceramic green sheets are substantially identical in their dimensions. The second ceramic green sheet has a window at a central region thereof. This window serves as a closed hollow space after an assembling operation of ceramic green sheets according to which the second ceramic green sheet is laminated between two first ceramic green sheets.
A slurry, forming a green adhesive layer, is applied on a peripheral region of each of the first ceramic green sheets. Then, the second ceramic green sheet is laminated between the first ceramic green sheets to bond them via the green adhesive layer, thereby forming a green laminate body with a closed hollow space therein.
Next, the green laminate body is degreased and sintered.
FIG. 12 shows a conventional ceramic laminate body 9 thus formed, according to which two first ceramic sheets 11 and 115 are bonded to the second ceramic sheet 12 via adhesive layers 93 and 935 so as to form a closed hollow space 10 between them (refer to the unexamined Japanese patent publication No. 59-29107).
However, the green adhesive slurry contains a great amount of organic binder compared with those involved in the first and second ceramic green sheets. In general, the organic binder is necessary to enhance the bonding or adhesive force.
Due to the presence of this organic binder, the green adhesive layer has a relatively low density in the initial condition. When the green adhesive layer is subjected to the degreasing and sintering processes, the adhesive layer contracts greatly.
The contraction of the adhesive layers possibly causes peeling of the ceramic sheets or generates voids. FIG. 12 shows cracks 99 appearing in the vicinity of the adhesive layers, which are caused by the contraction difference between the adhesive layers and the ceramic sheets.
An object of the present invention is to provide a ceramic laminate body which is free from cracks or any peeling-off phenomenon derived from a thermal contraction difference between adhesive layers and ceramic sheets.
Another object of the present invention is to provide a method for manufacturing this ceramic body.
Still another object of the present invention is to provide an application of this ceramic laminate body to a gas sensor.
In order to accomplish these and other related objects, the present invention provides a first ceramic laminate body comprising a first ceramic sheet and a second ceramic sheet which are bonded via an adhesive layer so as to form a closed hollow space between the first ceramic sheet and the second ceramic sheet. A tapered portion with a slant surface is formed at an inner end of the adhesive layer so as to protrude into the closed hollow space. A thickness t1 of the adhesive layer is equal to or smaller than 40 xcexcm, and a protruding length L1 of the tapered portion is equal to or larger than 2.5 t1.
Preferably, the thickness t1 of the adhesive layer is in a range from 20 xcexcm to 40 xcexcm.
Furthermore, the present invention provides a second ceramic laminate body comprising a first ceramic sheet and a second ceramic sheet which are bonded via an adhesive layer so as to form a closed hollow space between the first ceramic sheet and the second ceramic sheet, wherein a tapered portion with a slant surface is formed at an inner end of the adhesive layer so as to retract at least partly in a gap for the adhesive layer formed between the first and second ceramic sheets. A thickness t1 of the adhesive layer is within a range from 10 xcexcm to 40 xcexcm. An extended length L13 of the tapered portion is equal to or larger than 2.5 t1. And, the following relationship is established:
0 less than L12 less than 0.5 L11
where L11 represents an overall longitudinal length of the adhesive layer, and L12 is a retraction length of the tapered portion.
Furthermore, the present invention provides a first gas sensing element comprising a sensor section for measuring a gas concentration of a measured gas, and a support for supporting the sensor section. The sensor section comprises a solid electrolytic layer, and a pair of electrodes formed on opposite surfaces of the solid electrolytic layer. The support has a recessed portion defining a closed hollow space when the support is assembled with the sensor section. An adhesive layer is interposed between the sensor section and the support to bond a surface of the solid electrolytic layer to a surface of the support so that the closed hollow space is formed between the solid electrolytic layer and the support. A tapered portion with a slant surface is formed at an inner end of the adhesive layer so as to protrude into the closed hollow space. A thickness t1 of the adhesive layer is equal to or smaller than 40 xcexcm, and a protruding length L1 of the tapered portion is equal to or larger than 2.5 t1.
Furthermore, the present invention provides a second gas sensing element comprising a sensor section for measuring a gas concentration of a measured gas, and a support for supporting the sensor section. The sensor section comprises a solid electrolytic layer, and a pair of electrodes formed on opposite surfaces of the solid electrolytic layer. The support has a recessed portion defining a closed hollow space when the support is assembled with the sensor section. An adhesive layer is interposed between the sensor section and the support to bond a surface of the solid electrolytic layer to a surface of the support so that the closed hollow space is formed between the solid electrolytic layer and the support. A tapered portion with a slant surface is formed at an inner end of the adhesive layer so as to retract at least partly in a gap for the adhesive layer formed between the sensor section and the support. The thickness t1 of the adhesive layer is within a range from 10 xcexcm to 40 xcexcm. An extended length L13 of the tapered portion is equal to or larger than 2.5 t1, and the following relationship is established:
0 less than L12 less than 0.5 L11
where L11 represents an overall longitudinal length of the adhesive layer, and L12 is a retraction length of the tapered portion.
Moreover, the present invention provides a first method for manufacturing a ceramic laminate body, comprising the steps of forming a green laminate body by laminating a first ceramic green sheet and a second ceramic green sheet via a green adhesive layer so as to form a closed hollow space between the first and second ceramic green sheets, and sintering the green laminate body, wherein a tapered portion with a slant surface is formed at an inner end of the green adhesive layer so as to protrude into the closed hollow space, a thickness t0 of the green adhesive layer is within a range from 40 xcexcm to 80 xcexcm, and a protruding length L0 of the tapered portion is equal to or larger than 2 t0.
The present invention provides a second method for manufacturing a ceramic laminate body, comprising the steps of forming a green laminate body by laminating a first ceramic green sheet and a second ceramic green sheet which are bonded via a green adhesive layer so as to form a closed hollow space between the first and second ceramic green sheets, and sintering the green laminate body, wherein a tapered portion with a slant surface is formed at an inner end of the green adhesive layer so as to retract at least partly in a gap for the green adhesive layer formed between the first and second ceramic green sheets, a thickness t0 of the green adhesive layer is within a range from 20 xcexcm to 80 xcexcm, an extended length L03 of the tapered portion is equal to or larger than 2 t0, and the following relationship is established:
xe2x80x830 less than L02 less than 0.5 L01
where L01 represents an overall longitudinal length of the green adhesive layer, and L02 is a retraction length of the tapered portion.